This invention relates to a method and apparatus for producing a diffraction grating master for use in producing optical gratings by an embossing technique.
Recent developments in financial systems, credit systems, security systems, and funds transfer systems rely heavily on the use of record media or "credit cards" having magnetic stripes or tracks thereon with various data like account number, credit limits, credit status, credit available for use, and the like being recorded magnetically on the stripes. Such systems have to be designed to avoid or minimize the fraudulent use of such credit cards.
One of the ways in which fraudulent use of such credit cards is made is to counterfeit the cards by mass reproduction techniques which "skim" or transfer the data magnetically recorded on a valid card to a fraudulent one.
The problem of trying to prevent the unauthorized duplication of or use of valid credit cards used in financial systems and the like is a very extensive one as evidenced by the variety of different techniques tried to avoid the problem. Some representative techniques are disclosed in the following U.S. Pat. Nos. 3,604,901; 3,620,590; 3,644,716; 3,759,179; 3,790,754; 3,808,404; 3,831,008; 3,401,830; 3,697,729, and 3,691,527.
A copending application Ser. No. 588,937, filed on June 20, 1975 and assigned to the same assignee as this application discloses a system for checking on the validity of credit cards used in financial systems and the like by using a credit card which has first data recorded thereon in the form of optical gratings and second data which is recorded in a magnetic stripe or track on the card. When the card is used in such a system, the first data is read by an optical grating reading means and the second data is read by a conventional magnetic track reader. The first and second are then compared to determine the validity of the card being used in the system, and a validity signal is issued depending upon whether the card was valid or not. Because the first data is made up of optical gratings which are embedded in the credit card itself, the optical gratings are tamperproof and can not be easily skimmed or counterfeited as data which is magnetically recorded on a card can be. Thus, a system was disclosed in said copending application which prevented the mass counterfeiting of valid credit cards.
A second copending application Ser. No. 611,378 filed by William R. Horst, Charles F. Mort and William J. Hale, on the same date as this application and assigned to the same assignee as this application, discloses an optical identification system including a reader for reading superimposed optical gratings located in a grating plane on a record medium. This optical identification system and reader are an improvement on the system and reader disclosed in said first copending application in that the use of superimposed gratings enhances the security of the system, and the reader is less susceptible to erroneous readings when the gratings being read are positioned slightly out of the associated reading or grating plane.
This invention relates to a method and apparatus used for producing a diffraction rating master for producing superimposed optical or diffraction gratings by an embossing technique.
Most of the prior art techniques for producing diffraction gratings utilize ruling engines; one such ruling engine is shown in U.S. Pat. No. 3,382,761, for example. A second prior art technique for producing an optical diffraction grid employs photographic and chemical machining techniques as shown in U.S. Pat. No. 3,728,117.
One of the problems with producing superimposed diffraction gratings by the ruling engine technique is that generally only soft metals like aluminum or silver can be ruled thereby, and consequently, diffraction rating masters made from such metals are not sufficiently durable when used to produce diffraction gratings by an embossing technique. Also, when superimposed gratings are made by a ruling engine, the grooves of one of the gratings seem to "chip" or tear into the grooves of the other, especially when gratings having a high line pitch or number of lines per mm. are made.
None of the references cited discloses the method and apparatus of this invention for producing a diffraction grating master which in turn can be used for producing diffraction gratings by an embossing technique.